The present invention relates to the reception of Binary Phase Shift Keying (BPSK) signals, as well as subcarrier modulated signals, such as Binary Offset Carrier (BOC) modulated signals, but not limited thereto. In particular, the present document relates to the determination of a Carrier-to-Noise ratio (or a Signal-to-Noise Ratio) of signals in a Global Navigation Satellite System (GNSS).
In next generation GNSS systems, binary offset carrier (BOC) modulation and multiplexed binary offset carrier (MBOC) modulation will be used. Examples for such BOC or MBOC modulated signals are the Galileo E1 open signal, a CBOCc(6,1,1/11) signal (i.e. a composite BOC signal using a cosine subcarrier), the Galileo PRS (Public Regulated Service) signals on E1 and E6, a BOCc(15,2.5) signal and a BOCc(10,5) signal, respectively, and the GPS M-code, which corresponds to a BOC(10,5) signal. In more general terms, the above mentioned signals may be referred to as subcarrier modulated signals. Such subcarrier modulated signals comprise a carrier signal, which is modulated with a pseudo random noise (PRN) code, and which is additionally modulated with one or more subcarriers. Additionally, navigation message data may or may not be modulated onto the carrier signal.
A BOC modulated signal without subcarrier modulation corresponds to a BPSK (Binary Phase Shift Keying) signal used for GPS SPS (Standard Positioning System), which exhibits a triangular autocorrelation function. FIG. 1a shows an example subcarrier signal 101, 102 having a subcarrier symbol duration
            T      s        =          1              2        ⁢                                  ⁢                  f          s                      ,wherein fs is the subcarrier rate. FIG. 1a also illustrates the symbol duration
      T    c    =      1          f      c      of a symbol of the PKN code (wherein fc is the code rate), yet the PRN code signal itself is not shown in this figure. In the illustrated example, the subcarrier rate fs is twice as high as the code rate fc and the resulting BOC signal is referred to as a BOC(2m,m) signal (based on the notation BOC(m,n) where the respective frequencies are given by fs=m·1.023 MHz, fc=n·1.023 MHz). The code rate fc may also be referred to as the chip rate and a symbol of the PRN code (having a code symbol duration Tc) may be referred to as a chip. The subcarrier 101, 102 itself has a saw-tooth like autocorrelation function 103 as shown in FIG. 1a. The autocorrelation function 113 of a BOC signal is approximately given by the multiplication of a triangular PRN-code autocorrelation function 123 with the subcarrier autocorrelation function 103. Therefore, this autocorrelation function 113 has multiple peaks as shown in FIG. 1b. 
A receiver in a GNSS typically receives signals from a plurality of different satellites, i.e. via a plurality of different channels. Typically, a pre-determined number of received channels (e.g. three channels) are used to determine the position of the GNSS receiver. If more than the pre-determined number of received channels is received, the receiver may be configured to select a subset of the received channels. The precision of the determined position of the receiver may be increased by selecting those channels having the relatively highest Carrier-to-Noise Ratio (C/N0) and/or the relatively highest Signal-to-Noise Ratio (SNR) among the received channels. Hence, it is desirable to provide a scheme for reliably and precisely estimating the C/N0 and/or the SNR of a received channel within a GNSS.
Exemplary embodiments of the present invention are directed to schemes for reliably and precisely estimating the C/N0 and/or the SNR of satellite signals, which schemes are particularly beneficial for the estimation of C/N0 and/or SNR values, which exceed a pre-determined threshold (e.g. 50 dbHz).